Oxygen-deficient GdK2Nb5O15 ferroelectric epitaxial thin film B. Allouche, Y. Gagou, F. Le Marrec, M.-A. Fremy and M. El Marssi EPL, 116 6 (2016) 67001 Published online: 06 February 2017 DOI: 10.1209/0295-5075/116/67001